I/Q Modulator and Demodulator with Wide Instantaneous Bandwidth and High Local-Oscillator-Port-to-Radio-Frequency-Port Isolation

ABSTRACT

An improved quadrature modulator/demodulator (IQMD) may use two-phase quadrature local oscillator (LO) signal generation for generating 0° and 90° LO signals, and an anti-phase combiner/divider (at 0° and 180°) on the RF (radio frequency) port. The IQMD may include mixers (which may be double-balanced passive mixers) that function as downconverters when a signal is incident at their radio frequency (RF) ports, and function as upconverters when signals are incident on their intermediate frequency (IF) ports. Accordingly, the IQMD may function as an I/Q modulator by connecting digital-to-analog converters (DAC) to the differential I and Q ports, and/or it may also function as an I/Q demodulator by connecting analog-to-digital converters (ADC) to the differential I and Q ports.

PRIORITY CLAIM

This application is a continuation of U.S. patent application Ser. No.14/879,285 titled “I/Q Modulator and Demodulator with Wide InstantaneousBandwidth and High Local-Oscillator-Port-to-Radio-Frequency-PortIsolation”, filed on Oct. 9, 2015 and hereby incorporated by referenceas though fully and completely set forth herein.

FIELD OF THE INVENTION

The present invention relates to the fields of wireless communicationand instrumentation, and more particularly to the design of an I/Qmodulator and demodulator.

DESCRIPTION OF THE RELATED ART

Wireless communication systems are rapidly growing in usage. In recentyears, wireless devices such as smart phones and tablet computers havebecome increasingly sophisticated. In addition to supporting telephonecalls, many mobile devices now provide access to the internet, email,text messaging, and navigation using the global positioning system(GPS), and are capable of operating sophisticated applications thatutilize these functionalities.

Digital wireless communications are typically implemented through theuse of modulators and demodulators, which provide a necessary RF (radiofrequency) interface for systems such as cordless phones, wirelessnetworks, and wireless peripheral devices for computers, in addition totest and control systems that may use a wireless interface to couplecertain system elements. One commonly used modulation method that lendsitself well to digital processes is “quadrature modulation”, whichemploys two carriers out of phase by 90° and modulated by separatesignals. This modulation technique is also referred to as “I/QModulation”, where “I” refers to the “in-phase” component of thewaveform, and “Q” refers to the quadrature component, or90°-out-of-phase component of the waveform. In its various forms, I/Qmodulation provides an efficient way to transfer information, and alsoworks well with digital formats. An I/Q modulator may be used foramplitude modulation (AM), frequency modulation (FM) and phasemodulation (PM). There are also many digital encoding standards thatallow for the transmission of vast amounts of data over wireless RFinterfaces in shorter periods of time.

The development of next generation wireless systems calls for increaseddata transfer capabilities. One example of a next generation standard is5G (5th generation mobile networks or 5th generation wireless systems)which represents the next major phase of mobile telecommunicationsstandards beyond the current 4G/IMT-Advanced standards. One essentialgoal for 5G systems is to deliver increased capacity for cellularaccess, with a rough goal of approximately 10 Gbps (10 gigabits persecond) peak data rates and 100 Mbps (100 megabits per second) at celledges. Possible schemes of achieving increased capacity include highrank MIMO (multiple input multiple output) and beamforming techniques,higher order modulation schemes, and increased instantaneous bandwidth(IBW), or some combination of each. Increased IBW is also beneficial forother systems in which wireless data transmission may be a less costlysolution than installation of fiber optic systems. Such systems includecellular front-haul (the connection from remote radio heads to basestation controllers), cellular backhaul (the connection from the mobilenetwork to the wired network), and point-to point radio links. Large IBWalso enables high capacity short range radio links in the 60 GHz rangedue to atmospheric oxygen absorption. The applications for these linksare wireless LAN (local area network; e.g. IEEE 802.11ad) and wirelesstransmission of high-definition video, as well as cellular backhaul,cellular access, Wi-Fi offloading, connector free platform extension(wireless docking), device-to-device collaboration, multi-media kiosks,and wireless PCIe extension.

I/Q modulators and demodulators are key components of modern digitalradio systems because they offer potentially higher levels ofintegration due to decreased reliance on high-Q filters as required bysuper-heterodyne systems. Additionally, I/Q modulation and demodulationis advantageous for systems with high IBW because twice the IBW can beachieved for the same sample rate as compared with super-heterodynesystems that employ intermediate frequency (IF) sampling. Unfortunately,most I/Q modulators and demodulators come with their own set ofimpairments such as DC offsets, I/Q mismatch, even-order distortion,flicker noise, and LO (local oscillator) leakage (from the LO port tothe RF port) that can reduce the dynamic range of digital radio systemsthat employ them. LO leakage reflecting back into modulator/demodulatorresult in DC offsets via self-mixing. These static DC offsets can becorrected using DSP (digital signal processing) techniques at theexpense of decreased dynamic range.

In systems using orthogonal frequency division multiplexing (OFDM), thesub-carriers near DC are often left unused such that it is more tolerantof DC offsets. Unlike OFDM single carrier modulation is susceptible toDC offsets. However, single-carrier modulation is preferred in highfrequency wide IBW systems over OFDM due to lower peak-to-average powerratio which decreases the linearity requirement on power amplifiersleading to reduced power consumption and higher efficiency. Poweramplifier linearity and efficiency are especially important atmillimeter wave frequencies where the available spectrum exists tosupport communications links with large IBW, but low cost CMOS poweramplifiers have difficulty providing the required transmit power. Inaddition to static DC offsets, LO leakage that radiates off the receiverantenna and reflects off an external obstruction which is movingrelative to the receiver can cause time-varying DC offsets. Finally, LOleakage can be amplified by the transmitter's power amplifier and makeit difficult for receiver to demodulate. Thus, radio standards such as802.11ad specify that the power at the carrier frequency must besignificantly less than total signal power.

Most present day solutions employ multiple mixers and LO distributionnetworks with proper phase relationships in order to decrease LO leakageand the DC offsets resulting from self-mixing. In some systems, fourmixers are employed and are connected using four-phase quadrature LOgeneration (0°, 90°, 180°, and 270°) and an in-phase RFdivider/combiner. Some of these systems feature a single node that tiesthe RF ports of the four mixers together, which is suitable forintegrated circuits. Some systems use a suitable in-phase combiningnetwork which is more appropriate for printed circuit boards wherelonger lengths between mixers are required. In both cases, LO signalswhich leak to the RF ports of the mixers due to the non-infiniteLO-to-RF isolation are summed at the RF port of the modulator ordemodulator. Specifically, the 0° and 180° LO leakage signals canceleach other, and the 90° and 270° LO leakage signals cancel each other.

Other corresponding issues related to the prior art will become apparentto one skilled in the art after comparing such prior art with thepresent invention as described herein.

SUMMARY OF THE INVENTION

Various embodiments of an improved I/Q modulator/demodulator (IQMD)feature a modulator and demodulator topology which utilizes a two-phasequadrature LO (local oscillator) signal generation process for providing0° LO signals and 90° LO signals, and further feature an anti-phasecombiner/divider (0° and 180°) on the RF (radio frequency) port. TheIQMD may include mixers (in some embodiments, double-balanced passivemixers) that function as downconverters when a signal is incident ontheir RF ports or they may function as upconverters when signals areincident on their IF (intermediate frequency) ports. Thus, the IQMD mayequally function as an I/Q modulator, when digital-to-analog converters(DAC) are connected to the differential I and Q ports, and as an I/Qdemodulator when analog-to-digital converters (ADC) are coupled to thedifferential I and Q ports.

The IF port of the mixer (hereinafter also simply referenced as “mixer”)may be most often DC-coupled. Therefore, embodiments of the IQMD mayaccommodate modulated signals with baseband frequency content at 0 Hz.Another feature of the mixer may be a wide bandwidth on its IF port,thus allowing the IQMD to handle signals with very wide instantaneousbandwidth. As opposed to single-ended I/Q modulators and demodulators,the differential baseband ports are convenient for connecting to DACsand ADCs, as they usually have differential analog outputs and inputs,respectively. The use of differential signaling provides substantialbenefits such as cancellation of even-order intermodulation distortion,immunity to far-field radiation, and common-mode rejection ofinterfering signals. The LO and RF ports of the IQMD topology may remainsingle-ended, making it convenient to interface with typicalhigh-frequency circuits.

In addition to the mixers, various embodiments of an IQMD circuit mayinclude several other functional blocks. In one set of embodiments, theIQMD may include a first circuit (which may be a 180° hybrid circuit4-port circuit) that, when excited by an RF signal at a first port (alsoreferred to as a “delta” port), may generate signals at a third port(also referred to as a “+” port) and a fourth port (also referred to asa “−” port). The generated signals may be power attenuated by aspecified amount (e.g. 3 dB), and may be out of phase (e.g. by 180°)with respect to each other. If the first circuit is instead excited by asignal at a second port (also referred to as a “sum” port), thegenerated signals at the third (“+”) port and fourth (“−”) port may eachbe attenuated by a specified amount (e.g. 3 dB), and may be in phase, or0° degrees out of phase. If the first circuit is excited at the third(“+”) and fourth (“−”) ports with two signals that have the same phaseand equal magnitude, then the signals may appear at the second (“sum”)port because they are added, and no signal may appear at the first(“delta”) port because they are subtracted. Likewise, if the firstcircuit is excited at the third (“+”) and fourth (“−”) ports with twosignals that are 180° out of phase and have the same magnitude, then thesignal may be added at the first (“delta”) port and no signal may appearat the second (“sum”) port.

At the LO port input, the IQMD may include a 0° power divider. Whenexcited at the LO port, the power divider may output two signals whichare each attenuated by a specified amount (e.g. 3 dB) and have the samephase. It should be noted that the power divider circuit may alsofunction as a power combiner for signals that are in-phase and are ofequal magnitude. A respective second circuit, which may be a 90° hybridcircuit, may be connected to the oscillator port of each mixer. Thesecond circuit may be a 3-port circuit which, when excited by a signalat its input port, may generate two respective output signals that are90° out-of-phase. In some embodiments, the second circuit may be 4-porthybrid circuit that also includes an isolation port terminated in aresistive load.

The IQMD circuit may operate as either a modulator or demodulator. Whencombined with analog-to-digital converters (ADCs) on the respectivedifferential “I” and “Q” ports (i.e. on the differential pair of I portsand the differential pair of Q ports), the IQMD may function and operateas an I/Q demodulator. In this mode of operation, a signal may beprovided to the RF port and may be split into two signals of oppositepolarity on the third and fourth ports of the first circuit. The splitsignals may be further split, in phase, and each phase-split signal maybe provided into the input of a respective corresponding one of themixers. The LO signal may be provided to an in-phase power divider andthe power-divided LO signals may be provided to respective secondcircuits that drive each mixer with two sets of signals that areseparated by 0 or 90 degrees. When the RF and LO signals combine in themixers, the respective baseband signals at the I port and ˜I (i.e. “notI”) port have the same magnitude while being 180° out of phase withrespect to each other, that is, the amplitude of the signal at the Iport is commensurate with the amplitude of the signal at the ˜I port,while there is a 180° phase difference between the signal at the I portand the signal at the ˜I port. The respective baseband signals at the Qport and ˜Q (i.e. “not Q”) port also have the same magnitude and are180° out of phase with respect to each other, that is, the amplitude ofthe signal at the Q port is commensurate with the amplitude of thesignal at the ˜Q port, while there is a 180° phase difference betweenthe signal at the Q port and the signal at the ˜Q port. Furthermore,there may be a phase difference of 90° between I and Q (and ˜I and ˜Q),respectively. With these relative phase shifts and appropriate digitalsignal processing, digitally modulated signals may be demodulated.

When the IQMD circuit is operated as an I/Q modulator, the incidentbaseband signals may be provided on the differential “I” and “Q” portsand the RF port may be used as the output port. The operation of thecircuit is similar as described above with respect to operating the IQMDas a demodulator, except that the signal is flowing in the oppositedirection. It should be noted that the mixers may not have infiniteisolation between their respective LO ports and RF ports, which mayresult in the LO signal leaking into the RF path. In the case of an I/Qmodulator, the LO signal may fall at the center of the instantaneous RFbandwidth. If the LO signal is too large, it may prevent thecorresponding I/Q demodulator at the other end of the wireless link fromdemodulating the signal. In various embodiments of the IQMD circuit, therespective LO signals that leak from the respective LO ports of themixers associated with the pair of differential in-phase ports to thethird and fourth ports of the first circuit, respectively, both have thesame relative phase. Thus, as these two signals enter the first circuit,they are dissipated into the load connected at the second port (or “sum”port) of the first circuit instead of emanating out of the first port(or “delta” port). The same is true for signals which leak from therespective LO ports of the mixers (associated with the pair ofdifferential quadrature ports) to the third and fourth ports of thefirst circuit, respectively. Hence, the LO-to-RF isolation of the I/Qmodulator may approximately equal to, or be within a specifiedpercentage of the sum (in dB) of the LO-RF isolation of each mixer andthe isolation of the first circuit.

Other aspects of the present invention will become apparent withreference to the drawings and detailed description of the drawings thatfollow.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when thefollowing detailed description of the preferred embodiment is consideredin conjunction with the following drawings, in which:

FIG. 1 shows a circuit diagram of first exemplary I/Qmodulator/demodulator, according to some embodiments;

FIG. 2 shows a circuit diagram of a second exemplary I/Qmodulator/demodulator, according to some embodiments;

FIG. 3 shows a partial circuit diagram of an exemplary I/Qmodulator/demodulator that uses a balun, according to some embodiments;

FIG. 4 shows a partial circuit diagram of an exemplary demodulatorconfiguration of the baseband ports for an I/Q modulator/demodulator,according to some embodiments;

FIG. 5 shows a circuit diagram of an exemplary I/Q modulator/demodulatorcircuit, according to some embodiments; and

FIG. 6 shows a partial circuit diagram of an exemplary transceiver thatuses multiple instances of I/Q modulators/demodulators, according tosome embodiments.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and are herein described in detail. It should beunderstood, however, that the drawings and detailed description theretoare not intended to limit the invention to the particular formdisclosed, but on the contrary, the intention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of an I/Q modulator/demodulator (IQMD) circuit describedherein may be used in a variety of systems and devices that use I/Qmodulation/demodulation. Such devices and systems include systemsdesigned to perform test and/or measurement functions, to control and/ormodel instrumentation or industrial automation hardware, or to model andsimulate functions, e.g., modeling or simulating a device or productbeing developed or tested, etc. Embodiments of the IQMD circuit may alsobe included in various radio frequency (RF) devices such as wirelesscommunication devices (e.g. cellular phones, tablets, wearable devicessuch as smart watch and smart glasses, etc.). More specifically,embodiments of the disclosed IQMD may be used in various instances wheremodulation/demodulation, more specifically I/Q modulation/demodulationof signals is performed. However, it is noted that various embodimentsmay be used for a variety of applications, and such applications are notintended to be limited to those enumerated above. In other words,applications discussed in the present description are exemplary only,and various embodiments of I/Q modulator/demodulator circuits withdifferential baseband may be used in any of various types of systems.

FIG. 1 shows a circuit diagram of an exemplary I/Q modulator/demodulator(IQMD) 300 according to some embodiments. IQMD 300 may feature amodulator and demodulator topology that utilizes two-phase quadrature LOgeneration, using a local oscillator (LO) input (19) and circuits 306and 312 for generating 0° and 90° phase LO signals. The IQMD 300 mayfurther include an anti-phase combiner/divider circuit 302 for combiningout-of-phase signals present on ports 3 and 4 onto port 1, andterminating in-phase signals at port 3 and 4 onto the load connected toport 2. The IQMD 300 may also include mixers 304, 308, 310 and 314 thatmay function as downconverters when a signal is provided at theirrespective RF ports (5-8), and may also function as upconverters whensignals are provided at their IF (intermediate frequency) ports (15-18).The IQMD may thereby function as an I/Q modulator by couplingdigital-to-analog converters (DAC) to the differential I and Q ports(15-18), or it may function as an I/Q demodulator by couplinganalog-to-digital converters (ADC) to the differential I and Q ports(15-18). The differential I ports (15, 17) are also referred to hereinas differential in-phase ports, and differential Q ports (16, 18) arealso referred to herein as differential quadrature ports.

The respective IF ports (15-18) of mixers 304, 308, 310 and 314 may beDC-coupled or they may be AC coupled, and various embodiments of theIQMD 300 may accommodate modulation formats with no information centeredat 0 Hz. Furthermore, the respective IF ports (15-18) of mixers 304,308, 310 and 314 may be wide bandwidth ports, allowing the IQMD 300 tohandle signals with very wide instantaneous bandwidth. In contrast tosingle-ended I/Q modulators and demodulators, differential basebandports may be used to connect to DACs and ADCs, as DACs usually havedifferential analog outputs and ADCs usually have differential analoginputs. The use of differential signaling may facilitate cancellation ofeven-order intermodulation distortion, immunity to far-field radiation,and common-mode rejection of interfering signals. The LO port (19) andRF port (1) of IQMD 300 may remain single-ended, allowing IQMD 300 toconveniently interface with high-frequency circuits that are most oftensingle-ended.

In addition to the mixers 304, 308, 310 and 314, embodiments of IQMDcircuit 300 may include several other functional blocks as shown inFIG. 1. For example, IQMD 300 may include a first circuit 302 (in someembodiments, a 180 degree or 180° hybrid circuit), which may featurefour ports. When excited by an RF signal at a first port (also referredto as a “delta” port, and indicated by the numeral ‘1’), first circuitmay output signals at a third port (also referred to as a “+” port, andindicated by the numeral ‘3’) and a fourth port (also referred to as a“−” port, and indicated by numeral ‘4’). The output signals at ports 3and 4 may be power attenuated by a specified amount (e.g. 3 dB), and maybe out of phase with respect to each other, e.g. by 180°. If the firstcircuit 302 is instead excited by a signal at a second port (alsoreferred to as a “sum” port, and indicated by numeral ‘2’), the outputsignals at the third (“+”) port and fourth (“−”) port may each beattenuated by a specified amount (e.g. 3 dB), and may be in phase, or 0°degrees out of phase. It should be noted, however, that as shown in FIG.1 (and also FIG. 2), the port 2 is terminated, and is therefore notconfigured to be functionally excited by a signal as opposed to port 1.If the first circuit is excited at the “+” (3) and “−” (4) ports withtwo signals of the same phase and of equal magnitude, then the sum ofthose two signals may therefore appear at the “sum” (2) port, and nosignal may appear at the “delta” (1) port, resulting from the differenceof the two signals trending to zero. Similarly, if the first circuit 302is excited at the “+” (3) port and the “−” (4) port with two signals,respectively, that are 180° out of phase with respect to each other andhave the same magnitude, then the two signals may be added at the“delta” (1) port and no signal may appear at the “sum” (2) port.

The IQMD 300 may also include a 0° power divider 316 at the LO portinput (19). When excited at the LO port (19), the power divider mayoutput two signals at ports 13 and 14. The signals output by powerdivider 316 may each be attenuated by a specified amount (e.g. 3 dB) andmay both have (or they both may be of) the same phase. It should benoted that the power divider circuit 316 may also function as a powercombiner for signals that are in-phase and are of equal magnitude,though circuit 316, as shown in the figures is not used in that manner.Respective second circuits 306 and 312 (in some embodiments, 90° hybridcircuits also having an isolation port—not shown—terminated in aresistive load) may be connected to corresponding oscillator ports ofeach mixer circuit 304, 308, 310 and 314 as shown. Each second circuit(306 and 312) may have three ports. It should be noted, however, thatthe second circuits (306 and 312) may be 90° hybrid circuits that mayhave a fourth port, specifically an isolation port, which may beterminated with a resistive load for the purposes of operation disclosedherein. When excited by a signal at its respective input port (inputport 13 for second circuit 306, and input port 14 for second circuit312), each second circuit (306 and 312) may generate two respectiveoutput signals (output signals 9 and 10 for second circuit 306, and 112and output signals 12 for second circuit 312) that are 90° out-of-phasewith respect to each other. The IQMD circuit 300 may operate as either amodulator or demodulator.

Operation of Various Embodiments of IQMD Circuits

Referring to at least FIGS. 1 and 2, the operation of variousembodiments of an IQMD circuit may be described as follows. Amodulator/demodulator (e.g. IQMD 300 or 350) may include an RF port(e.g. RF port), and may further include a first circuit (e.g. circuit302) having a first port (e.g. port 1) coupled to the RF port, andfurther having a second port (e.g. port 3) and a third port (e.g. port4). The first circuit may generate a pair of out-of-phase input signalsat the second port and third port, responsive to the first port beingexcited by a first signal received at the RF port, and may furthergenerate a summed output signal at the first port, responsive to thesecond port and the third port being excited by a pair of out-of-phaseoutput signals. The modulator/demodulator may also include a first mixer(e.g. a mixer that includes mixer circuits 304 and 306) coupled to thesecond port. The first mixer may downconvert a first out-of-phase inputsignal of the pair of out-of-phase input signals to a first pair ofincoming baseband signals (e.g. baseband signals received at ports 15and 16), and upconvert a first pair of outgoing baseband signals (e.g.baseband signals provided at ports 15 and 16) to a first out-of-phaseoutput signal of the pair of out-of-phase output signals. Themodulator/demodulator may further include a second mixer (e.g. a mixerthat includes mixer circuits 310 and 314) coupled to the third port. Thesecond mixer may downconvert a second out-of-phase input signal of thepair of out-of-phase input signals to a second pair of incoming basebandsignals (e.g. baseband signals received at ports 17 and 18), andupconvert a second pair of outgoing baseband signals (e.g. basebandsignals provided at ports 17 and 18) to a second out-of-phase outputsignal of the pair of out-of-phase output signals.

The modulator/demodulator may also include a local oscillator (LO) port(e.g. port 19) to receive an LO signal, and the first mixer and thesecond mixer may perform upconversion and/or downconversion based on theLO signal. The modulator/demodulator may also include a zero-phase powersplitter (e.g. power splitter 316) coupled to the LO port to receive theLO signal and derive a first LO signal (e.g. LO signal provided at port13) and a second LO signal (e.g. LO signal provided at port 14) from theLO signal, where the first LO signal and the second LO signal are inphase with respect to each other. The first mixer may performupconversion and/or downconversion based on the first LO signal, and thesecond mixer may perform upconversion and/or downconversion based on thesecond LO signal. In some embodiments, the modulator/demodulator mayinclude a phase shifter (e.g. phase shifter 362) coupled to the LO portto receive the LO signal and generate an in-phase LO signal (e.g. the LOsignal provided at port 20) and a quadrature LO signal (e.g. the LOprovided at port 21) based on the LO signal. The first mixer and thesecond mixer may each perform upconversion and/or downconversion basedon the in-phase LO signal and the quadrature LO signal.

In further embodiments, the modulator/demodulator may also include afirst zero-phase power splitter (e.g. power splitter 356) and a secondzero-phase power splitter (e.g. power splitter 364). The firstzero-phase power splitter may receive the in-phase LO signal and mayderive a first in-phase LO signal and a second in-phase LO signal fromthe in-phase LO signal. The second zero-phase power splitter may receivethe quadrature LO signal and derive a first quadrature LO signal and asecond quadrature LO signal from the quadrature LO signal. The firstmixer may then perform upconversion and downconversion using the firstin-phase LO signal and the first quadrature LO signal, and the secondmixer may perform upconversion and downconversion using the secondin-phase LO signal and the second quadrature LO signal.

In some embodiments, the first circuit may be a hybrid circuit thatfurther includes a fourth port (e.g. port 2), and may generate a secondsummed output signal at the fourth port, responsive to the second portand the third port being excited by a pair of in-phase output signals.It should be noted that in the various embodiments explicitly disclosedherein, port 2 is shown as being terminated with a resistor to ground.In some embodiments the first circuit may be a balun circuit (e.g. baluncircuit 402), with the first port of the first circuit being anunbalanced port of the balun circuit, and the second and third ports ofthe first circuit being balanced ports of the balun circuit.

In some embodiments, the first pair of incoming baseband signals mayinclude a first incoming in-phase baseband signal and a first incomingquadrature baseband signal, and the first pair of outgoing basebandsignals may include a first outgoing in-phase baseband signal and afirst outgoing quadrature baseband signal. Furthermore, the second pairof incoming baseband signals may include a second incoming in-phasebaseband signal and a second incoming quadrature baseband signal, andthe second pair of outgoing baseband signals may include a secondoutgoing in-phase baseband signal and a second outgoing quadraturebaseband signal. The first incoming in-phase baseband signal and thesecond incoming in-phase baseband signal may form an incoming pair ofdifferential in-phase baseband signals (e.g. signals I and ˜I), and thefirst incoming quadrature baseband signal and the second incomingquadrature baseband signal may form an incoming pair of differentialquadrature baseband signals (e.g. Q and ˜Q). In addition, the firstoutgoing in-phase baseband signal and the second outgoing in-phasebaseband signal may form an outgoing pair of differential in-phasebaseband signals (e.g. I and ˜I), and the first outgoing quadraturebaseband signal and the second outgoing quadrature baseband signal mayform an outgoing pair of differential quadrature baseband signals (e.g.Q and ˜Q).

In some embodiments, each mixer may include a first mixer circuit (e.g.mixer circuit 304 or mixer circuit 310) which may receive an in-phasebaseband signal when upconverting, and provide an in-phase basebandsignal when downconverting, and may also include a second mixer circuit(e.g. mixer circuit 308 or mixer circuit 314) which may receive aquadrature baseband signal when upconverting, and provide a quadraturebaseband signal when downconverting. In some embodiments, the firstmixer circuit and the second mixer circuit may each be double-balancedpassive mixer circuits. Furthermore, in one set of embodiments, eachmixer may include a phase shifter circuit (e.g. phase shifter circuit306 or phase shifter circuit 312) which may generate an in-phaseoscillator signal and a quadrature oscillator signal based on a receivedlocal oscillator signal, provide the in-phase oscillator signal to thefirst mixer circuit and provide the quadrature oscillator signal to thesecond mixer circuit. The first mixer circuit may then performmodulation and demodulation using the in-phase oscillator signal, whilethe second mixer circuit may perform modulation and demodulation usingthe in-phase oscillator signal.

Demodulator Operation

Referring again to FIG. 1 (and/or FIG. 2), when combined withanalog-to-digital converters (ADCs) on the respective pair ofdifferential “I” ports (15, 17) and respective pair of differential “Q”ports (16, 18), IQMD 300 may function and operate as an I/Q demodulator.FIG. 4 shows a partial circuit diagram of an exemplary demodulatorconfiguration of the baseband ports (I, Q, and ˜Q) for IQMD 300,according to some embodiments. As seen in FIG. 4, ADC 512 is coupled tothe pair of differential in-phase ports (15, 17), while ADC 514 iscoupled to the pair of differential quadrature ports (16, 18) to providea demodulated digital baseband signal at the output of summing circuit518.

Referring again to FIG. 1, a signal may be provided to the RF port (1)and may be split into two signals of opposite polarity on nodes 3 and 4.The split signals may be further split, in phase, and each phase-splitsignal (at ports 3 and 4, respectively) may be provided into the inputof a respective corresponding one of the mixers 304, 306, 310, 314. TheLO signal (at node 19) may be provided to the in-phase power divider316, and the power-divided LO signals may drive each mixer (304, 306,310, 314) with two sets of signals that are separated by 0° or 90°. Whenthe RF and LO signals combine in the mixers 304, 306, 310, 314, therespective baseband signals at the pair of differential in-phase ports(15, 17) have the same magnitude and are 180° out of phase with respectto each other, that is, the amplitude of the signal at the I port (15)is commensurate with the amplitude of the signal at the ˜I port (17),while there is a 180° phase difference between the two signals. Therespective baseband signals at the pair of differential quadrature ports(16, 18) also have the same magnitude and are 180° out of phase withrespect to each other, that is, the amplitude of the signal at the Qport is commensurate with the amplitude of the signal at the ˜Q port,while there is a 180° phase difference between the two signals.Furthermore, there is a phase difference of 90° between I and Q (and ˜Iand ˜Q), respectively.

Modulator Operation

When the IQMD 300 circuit is operated as an I/Q modulator, the incidentbaseband signals may be provided on the pair of differential “I” ports(15, 17) and on the pair of differential “Q” ports (16, 18). In thiscase the RF port (1) may be used as the output port. The operation ofthe circuit is similar to the demodulator operation described above,with the difference that the signal is flowing in the oppositedirection, that is, from the two pairs of differential signal ports(15-18) to the RF port (1). It should be noted that mixers 304, 306,312, 314 may lack infinite isolation between their respective LO ports(9-12) and RF ports (5-8), which may result in the LO signal leakinginto the RF path. In the case of an I/Q modulator, the LO signal mayfall at the center of the instantaneous RF bandwidth. If the LO signalis too large, it may prevent a corresponding I/Q demodulator at theother end of the wireless link from demodulating the signal.

It is worth noting that when used as an I/Q modulator, embodiments ofIQMD circuit 300 (and 350) may operate to also reject common-modesignals that are present on the baseband differential pairs (I/˜I andQ/˜Q). For example, if a common-mode signal is present on thedifferential pair Q/˜Q and that common-mode signal is upconverted, thenit may appear at the RF ports of each I/Q mixer with the same amplitudeand phase and may thus be combined and dissipated in the 50Ω terminationon the sum port (i.e. the resistor coupled at port 2) of the firstcircuit 302.

Additional Considerations

It should further be noted that in various embodiments of IQMD circuit300, the respective LO signal that may leak from node 9 (via RF port 5)at mixer 304 to node 3 of circuit 302, and the respective LO signal thatmay leak from node 11 (via RF port 7) at mixer 310 to node 4 of circuit310, both have the same relative phase. Thus, as these two signalsappear at the first circuit (at ports 3 and 4), they may be dissipatedinto the load connected at terminal (or node) 2 of the first circuit 302instead of emanating out of RF port 1. The same is true for therespective LO signal that may leak from node 10 at mixer 308 (via RFport 6) to node 3 of circuit 302, and the respective LO signal that mayleak from node 12 (via RF port 8) at mixer 314 to node 4 of circuit 302.Hence, the LO-to-RF isolation of the IQMD circuit 300 may approximatelyequal to, or be within a specified percentage of the sum (in dB) of theLO-to-RF isolation of each mixer 304, 306, 312, 314 and the isolation ofthe first circuit 302.

Alternate Embodiments

FIG. 2 shows a circuit diagram of an alternate implementation 350 of anI/Q modulator/demodulator, according to some embodiments. The portnumbers in FIG. 2 correspond to the port numbers in FIG. 1 for each portnumber that is included in both figures. As shown in FIG. 2, as opposedto including two phase shifter circuits (such as circuits 306 and 312 inFIG. 1), circuit 350 includes a single phase shifter circuit 362, withits input connected to LO port 19 to receive the local oscillatorsignal. The circuit 362 may be excited by the LO signal, and responsiveto the LO signal, generate two respective output signals that are 90°out-of-phase with respect to each other. In other words, phase shiftercircuit 362 may generate an in-phase LO signal at port 20, and aquadrature LO signal at port 21. Thus, the in-phase oscillator signalmay be provided to a first 0° power divider 356 at port 20, and thequadrature oscillator signal may be provided to a second 0° powerdivider 364 at port 21. When excited at their respective input ports(20, 21), the power dividers may output respective pairs of signals atports 9 and 11, and 10 and 12. Each respective pair of signals output bythe power dividers (356 and 364) includes two respective signals thatmay be attenuated by a specified amount (e.g. 3 dB) and may be in phasewith respect to each other. For example, the pair of signals output bypower divider 356 at ports 9 and 11 may be in phase with respect to eachother, and/or they may each be attenuated by a specified amount. Thesame holds for power divider 364.

In this manner, rather than splitting the LO signal into two LO signals,and using two respective phase shifter circuits for phase shifting eachof the two LO signals to generate a respective in-phase LO signal and arespective quadrature LO signal for each pair of I/Q signals (asperformed in circuit 300), in embodiments exemplified in FIG. 2, asingle phase shifter circuit 362 is used to generate an in-phase LOsignal and a quadrature LO signal, which are then each divided/split toprovide the appropriate respective in-phase LO signals and respectivequadrature LO signals for the respective mixers. For example, thein-phase LO signal provided by circuit 362 may be divided/split bydivider circuit 356 to provide in-phase LO signals to mixers 304 and 310corresponding to the pair of differential in-phase baseband signals.Similarly, the quadrature LO signal provided by circuit 362 at port 21may be divided/split by divider circuit 364 to provide quadrature LOsignals to mixers 308 and 314 corresponding to the pair of differentialquadrature baseband signals.

Thus, in some embodiments the LO signal may first be divided/split firstinto a first LO signal and a second LO signal, and respective pairs ofin-phase LO signals and quadrature LO signals may be generated from thefirst LO signal and the second LO signal, respectively, to provide theappropriate LO signals to the respective mixers. In other embodiments,an in-phase LO signal and a quadrature LO signal may first be generatedfrom the LO signal, and the in-phase LO signal and quadrature LO signalmay each be divided/split into respective first and second in-phase LOsignals and first and second quadrature LO signals to be provided to theappropriate respective mixers.

Exemplary IQMD Circuit According to One Set of Embodiments

FIG. 5 shows the circuit diagram of an exemplary implementation of theproposed I/Q demodulator according to some embodiments. The RF node (1)is shown on the left, the LO (carrier) input (19) is shown on the right,and the pairs of differential in-phase and quadrature baseband signalsare shown at ports 15-18, respectively. Again, the port numbers in FIG.5 correspond to the port numbers in FIG. 1 for each port number that isincluded in both figures. As previously mentioned, circuit 600 mayoperate as a modulator by exciting the baseband inputs and making the RFport (1) the output, or it may operate as a demodulator when the RF port(1) is used as an input and the baseband ports (15-18) are used asoutputs. The circuit 600 includes four sub-circuits. The firstsub-circuit is a 180° hybrid 502, the second sub-circuit is a first I/Qmixer 604 (including phase splitter circuit 306 and mixer circuits 304and 308), the third cub-circuit is a second I/Q mixer 606 (includingphase splitter circuit 312 and mixer circuits 310 and 314), and thefourth sub-circuit is an in-phase power divider 516. In the exemplarycircuit shown in FIG. 5, the hybrid circuit 502 is implemented as amicrostrip three-section rat-race 180° hybrid circuit. The sum port (2)of the hybrid circuit is terminated with R1, which may be practicallyformed by the parallel combination of two surface mount thin-filmresistors (e.g. two 0201 100Ω surface mount thin-film resistors). Thehybrid circuit 502 may be fabricated using microstrips (traces/lines)A-G, with a specified substrate height and dielectric constant (e.g.substrate height of 10 mil and a relative dielectric constant of 3.66).The in-phase power divider 516 may be implemented as two-sectionWilkinson combiner. The I/Q mixers may be surface mount GaAs MMICdouble-balanced mixers operating over a specified frequency range (e.g.a frequency range of 8.5 GHz to 13.5 GHz. In some embodiments, thehybrid circuit 502 may be shrunk using fractal techniques.

Design Advantages

Various embodiments of the IQMD design disclosed herein provide severaladvantages in addition to the ability to function as both a modulatorand/or a demodulator. High-speed analog baseband circuits are commonlyconstructed using differential methodologies. Differential circuitsoffer advantages such as immunity to common-mode noise and spurs, andeven-order rejection. Additionally, high-speed ADCs and DACs most oftenhave differential input and output interfaces. Simultaneously, RF andmicrowave circuits predominantly use single-ended 50Ω interfaces.Embodiments of the disclosed IQMD circuit conveniently accommodate both.In addition to providing a single-ended interface on the RF port, the180 degree hybrid circuit significantly improves the LO-to-RF isolationof the modulator/demodulator and decreases self-mixing.

Referring again to the exemplary implementation shown in FIG. 5, the LOsignal may be applied to both I/Q mixers 604 and 606 with the same phasevia the Wilkinson power divider 516. The LO signals may leak from the LOports to the RF ports of the I/Q mixers, as indicated by dashed arrowsK, L, M and N from the I/Q mixers 604 and 606, respectively, towardshybrid circuit 502. The amplitudes of the LO leakage signals (K, L, M,and N) may be reduced by the LO-to-RF isolation of each respective I/Qmixer 604 and 606. The phase and amplitude of signals K and M will beequivalent, as will the phase of signals L and N. Thus, the K and Msignals appear in-phase on ports 3 and 4 of the hybrid circuit 502, andmay be combined at port 2 and dissipated in R1 instead of appearing atthe RF port (1). Similarly, signals L and N may also be dissipated inR1. Therefore, the overall LO-to-RF isolation of IQMD 600 may besignificantly improved.

The LO-RF isolation improvement may also be achieved by replacing thefirst circuit 302 (or hybrid circuit 502) with a balun, as shown in FIG.3. Balun 402 is different from hybrid circuit 502, as a balun has aneven-mode reflection coefficient of ±1 while a 180 degree hybrid circuitmay typically have a reflection coefficient of zero for even-modeexcitation. Referring back to FIG. 5, signals K and M, as well assignals L and N may be considered even-mode signals which may bereflected back into the I/Q mixers 604 and 606. It should be noted thatthe reflected LO signals may re-mix in the I/Q mixers 606 and 606 withthe LO signal (a process referred to as self-mixing), and may createvoltages at DC and 2 f_(LO) (i.e. two times the LO frequency) on thebaseband ports 15-18.

In some embodiments, IQMD may be designed for a specified tuning range.For example, in some embodiments, the IQMD circuit may have a tuningrange of approximately 8.5 to 13.5 GHz. The tuning range may be limitedby the bandwidth of the circuit 502, the baluns in the I/Q mixers, andthe LO power divider. In order to extend the tuning range, these threecomponents may be extended. For example, in some embodiments,commercially available broadband I/Q mixers with RF/LO ranges exceedingthree octaves may be used. In some embodiments, decade bandwidth 180°hybrid circuits may be obtained using asymmetric stepped or taperedbackward-wave directional couplers. For example, in order to realizepractical coupling profiles, two 8.34 dB couplers may be coupled intandem. In order to maintain equal even and odd mode phase velocity,homogeneous stripline may be used. The couplers may be implemented ininhomogeneous dielectric (such as microstrip) using wiggly or serpentinetechniques for equalizing the even and odd mode phase velocities. In oneset of embodiments, the LO power divider 316 may be extended infrequency by using a multi-section stepped or tapered Wilkinson powerdivider. In other embodiments, a second 180 degree hybrid may be used,and the sum port (3) may be driven with the LO, while the delta port (1)is terminated. In addition, a 3-resistor power divider may also be used,which may benefit from a smaller size but may dissipate more LO power(relative to reactive power division) and may provide less isolation.

Benefits

I/Q modulators and demodulators with wide instantaneous bandwidth arekey circuit elements that enable digital radio systems with data ratesabove 1 Gbps (1 gigabits per second) in the millimeter-wave spectrum.Various embodiments of the IQMD topology disclosed herein features highLO-to-RF isolation, low DC offsets, and convenient interfaces for LO,RF, and baseband circuitry. In various embodiments, the IQMD may berealized using commercial off-the-shelf technology, and may be widelyused in numerous applications, exemplified by but not limited tomillimeter-wave digital radio systems.

Exemplary Transceiver Incorporating IQMD circuits

FIG. 6 shows a partial circuit diagram of an exemplary transceiver thatincludes I/Q modulators/demodulators, according to some embodiments.Instances of the IQMD circuit, such as those shown in FIGS. 1, 2, and 5,for example, and may be incorporated into a transceiver system capableof delivering a high encoded data rate at a specified carrier frequency,for example a data rate of 10.2 Gbps at a carrier frequency of 74 GHz.The transceiver circuit in FIG. 6 may include a transmitter sub-circuit620 and a receiver sub-circuit 630. In transmitter sub-circuit 620, thebaseband data may be modulated up to a specified first frequency (e.g.12 GHz) using I/Q modulators 652 and 654, both of which may be instancesof the IQMD detailed, for example, in FIG. 1, and operated as modulators(as previously detailed above). A super-heterodyne stage 662 may be usedto upconvert the signal to a specified second frequency (e.g. up to 74GHz). Similarly, in the receiver sub-circuit 630, the modulated signalmay be downconverted from the specified second frequency (e.g. from 74GHz) to an IF frequency (e.g. 12 GHz) through conversion stage 664, andthen converted to baseband using I/Q demodulators 656 and 658, both ofwhich may be instances of the IQMD detailed, for example, in FIG. 1, andoperated as demodulators (as previously detailed above).

As shown in FIG. 6, there are bandpass filters coupled to the respectiveRF and LO ports of the I/Q modulators 652 and 654 and I/Q demodulators656 and 658. One reason for filtering the LO signal is to eliminate highharmonic levels which have been shown to imbalance I/Q modulators. Onereason for filtering the RF signal is to protect the I/Q demodulators(656 and 658) from the higher-order images centered at integer multiplesof the carrier frequency, and to prevent the I/Q modulators (652 and654) from transmitting harmonics of the modulated signal. Another reasonfor the bandpass filters is to prevent unwanted signals (spurs) andnoise at baseband frequencies from entering the respective RF ports ofthe I/Q demodulators (656 and 658), travelling through the mixer to theIF port, and entering the baseband. This may be especially true if theexcess noise ratio at the respective RF inputs of the I/Q demodulators(656 and 658) is high at baseband frequencies (e.g. due to high gainand/or high noise affecting the signals prior to entering the I/Qdemodulators), or if the RF-to-IF isolation of the I/Q demodulators islow.

As shown in FIG. 6, the transceiver circuit may use two data streamssimultaneously at the same carrier frequency by utilizing bothhorizontal and vertical antenna polarization and 2×2 MIMO(multiple-input-multiple-output) processing. In some embodiments, thespecified encoded data rate (e.g. 10.2 Gbps) may be achieved using asingle-carrier 16-QAM (quadrature amplitude modulation) with RRCfiltering (α=0.3), 7/8 encoding, and a symbol rate of 1536 MBd. The DACsshown in FIG. 6 may implemented as 14-bit DACs while the ADCs shown inFIG. 6 may be implemented as 12-bit ADCs, and they may each be clockedat a sample rate of 3072 MHz (2×oversampling). The DC-offsets and I/Qmismatch may be improved using single-point corrections. It should benoted that the numeric values provided above as well as those providedin FIG. 6 are for illustration purposes only, and various embodimentsmay use different appropriate values as required for any givenimplementation.

Although the embodiments above have been described in considerabledetail, numerous variations and modifications will become apparent tothose skilled in the art once the above disclosure is fully appreciated.It is intended that the following claims be interpreted to embrace allsuch variations and modifications.

We claim:
 1. An apparatus comprising: a first circuit comprising a radiofrequency (RF) port; and a plurality of mixers comprising a first set ofports coupled to the first circuit, and further comprising a second setof ports, wherein the plurality of mixers are configured to: operate asdownconverters when signals are applied to the plurality of mixers atthe first set of ports; and operate as upconverters when signals areapplied to the plurality of mixers at the second set of ports.
 2. Theapparatus of claim 1, wherein the first circuit is configured to performat least one of the following: combine out-of-phase signals present onthe first set of ports onto the RF port; or terminate in-phase signalspresent on the first set of ports onto a load connected to the firstcircuit.
 3. The apparatus of claim 2, wherein the first circuit isconfigured to perform at least one of the following: generateout-of-phase input signals at the second set of ports, based on an inputsignal applied to the RF port; or generate a summed output signal at theRF port, based on out-of-phase output signals applied to the first setof ports.
 4. The apparatus of claim 1, wherein the first circuit furthercomprises: a second port coupled to a respective first pair of mixerports of the first set of ports; and a third port coupled to arespective second pair of mixer port of the first set of ports; whereinthe first circuit is configured to perform at least one of thefollowing: generate a pair of out-of-phase input signals at the secondport and the third port, in response to the RF port being excited by aninput signal; or generate a summed output signal at the RF port, inresponse to the second port and the third port being excited by arespective pair of out-of-phase output signals.
 5. The apparatus ofclaim 4, wherein the plurality of mixers comprise: a first mixercomprising the first pair of mixer ports, and configured to perform atleast one of the following: downconvert a first out-of-phase inputsignal of the pair of out-of-phase input signals to a first pair ofincoming baseband signals; or upconvert a first pair of outgoingbaseband signals to a first out-of-phase output signal of the pair ofout-of-phase output signals.
 6. The apparatus of claim 5, wherein theplurality of mixers comprise: a second mixer comprising the second pairof mixer ports, and configured to perform at least one of the following:downconvert a second out-of-phase input signal of the pair ofout-of-phase input signals to a second pair of incoming basebandsignals; or upconvert a second pair of outgoing baseband signals to asecond out-of-phase output signal of the pair of out-of-phase outputsignals.
 7. The apparatus of claim 1, further comprising: a localoscillator (LO) port configured to receive an LO signal; wherein theplurality of mixers are configured to: perform downconversion whenoperating as downconverters, based on the LO signal; and performupconversion when operating as upconverters, based on the LO signal. 8.The apparatus of claim 7, further comprising: a zero-phase powersplitter coupled to the LO port and configured to receive the LO signaland derive a first LO signal and a second LO signal from the LO signal,wherein the first LO signal and the second LO signal are in phase withrespect to each other; wherein a first mixer of the plurality of mixersis configured to perform upconversion and downconversion based on thefirst LO signal; and wherein a second mixer of the plurality of mixersis configured to perform upconversion and downconversion based on thesecond LO signal.
 9. The apparatus of claim 7, further comprising: aphase shifter coupled to the LO port and configured to receive the LOsignal an generate an in-phase LO signal and a quadrature LO signalbased on the LO signal; wherein a first mixer of the plurality of mixersand a second mixer of the plurality of mixers are each configured toperform upconversion and downconversion based on the in-phase LO signaland the quadrature LO signal.
 10. The apparatus of claim 9, furthercomprising: a first zero-phase power splitter configured to receive thein-phase LO signal and derive a first in-phase LO signal and a secondin-phase LO signal from the in-phase LO signal; and a second zero-phasepower splitter configured to receive the quadrature LO signal and derivea first quadrature LO signal and a second quadrature LO signal from thequadrature LO signal; wherein the first mixer is configured to performupconversion and downconversion using the first in-phase LO signal andthe first quadrature LO signal; and wherein the second mixer isconfigured to perform upconversion and downconversion using the secondin-phase LO signal and the second quadrature LO signal.
 11. Theapparatus of claim 1, wherein the plurality of mixers comprisedouble-balanced passive mixer circuits.
 12. A method for processingsignals, the method comprising: receiving first signals at a radiofrequency (RF) port and providing second signals at the RF port; whenreceiving the first signals at the RF port: generating out-of-phaseinput signals based on the received first signals, and applying theout-of-phase input signals to a first set of ports of a plurality ofmixers; and downconverting, by the plurality of mixers, the out-of-phaseinput signals to corresponding baseband signals; and when providing thesecond signals at the RF port: upconverting, by the plurality of mixers,outgoing baseband signals to corresponding out-of-phase output signals,and applying the out-of-phase output signals to the first set of ports;and generating summed output signals based on the out-of-phase outputsignals, and providing the summed output signals as the second signals.13. The method of claim 12, wherein the out-of-phase input signalscomprise a pair of out-of-phase input signals, and whereindownconverting by the plurality of mixers comprises: downconverting, bya first mixer of the plurality of mixers, a first out-of-phase inputsignal of the pair of out-of-phase input signals to a first pair ofincoming baseband signals of the corresponding baseband signals; anddownconverting, by a second mixer of the plurality of mixers, a secondout-of-phase input signal of the pair of out-of-phase input signals to asecond pair of incoming baseband signals of the corresponding basebandsignals.
 14. The method of claim 12, wherein the correspondingout-of-phase output signals comprise a pair of out-of-phase outputsignals, and wherein upconverting by the plurality of mixers comprises:upconverting, by a first mixer of the plurality of mixers, a first pairof outgoing baseband signals of the outgoing baseband signals to a firstout-of-phase output signal of the pair of the pair of out-of-phaseoutput signals; and upconverting, by a second mixer of the plurality ofmixers, a second pair of outgoing baseband signals of the outgoingbaseband signals to a second out-of-phase output signal of the pair ofthe pair of out-of-phase output signals.
 15. The method of claim 12,further comprising: generating a local oscillator (LO) signal; andperforming the downconverting and the upconverting based on thegenerated LO signal.
 16. The method of claim 15, further comprising:deriving a first LO signal and a second LO signal from the LO signal,wherein the first LO signal and the second LO signal are in phase withrespect to each other; wherein performing the downconverting and theupconverting based on the generated LO signals comprises: a first mixerof the plurality of mixers performing respective first portions of thedownconverting and the upconverting based on the first LO signal; and asecond mixer of the plurality of mixers performing respective secondportions of the downconverting and the upconverting based on the secondLO signal.
 17. A transceiver comprising: a first modulator/demodulator(MODEM) circuit; and a second MODEM circuit; wherein each MODEM circuitof the first MODEM circuit and the second MODEM circuit comprises: afirst circuit comprising a radio frequency (RF) port; and a plurality ofmixers comprising a first set of ports coupled to the first circuit, andfurther comprising a second set of ports, wherein the plurality ofmixers are configured to: operate as downconverters when signals areapplied to the plurality of mixers at the first set of ports; andoperate as upconverters when signals are applied to the plurality ofmixers at the second set of ports.
 18. The transceiver of claim 17,wherein the first circuit is configured to perform at least one of thefollowing: combine out-of-phase signals present on the first set ofports onto the RF port; or terminate in-phase signals present on thefirst set of ports onto a load connected to the first circuit.
 19. Thetransceiver of claim 17, wherein the first circuit is configured toperform at least one of the following: generate out-of-phase inputsignals at the second set of ports, based on an input signal applied tothe RF port; or generate a summed output signal at the RF port, based onout-of-phase output signals applied to the first set of ports.
 20. Thetransceiver of claim 17, further comprising: a plurality ofdigital-to-analog converters coupled to the first MODEM circuit andconfigured to provide unmodulated analog baseband signals to the firstMODEM circuit for the first MODEM circuit to operate as a modulator; anda plurality of analog-to-digital converters coupled to the second MODEMcircuit and configured to receive demodulated analog baseband signalsfrom the second MODEM circuit for the second MODEM circuit to operate asa demodulator.